Tight/sore left lower back after playing

I sometimes get a sore/tight left QL (quadratus lumborum) after playing - I'm a rightie. The physiotherapists I've seen have all confirmed it's the QL, but unfortunately none of them know much about tennis so I haven't been able to get any advice other than "stretch it before and after". It's a bit of a problem because a tight QL can cause sacro-iliac issues, which I unfortunately know about all too well...

Does anyone here have the same problem? Are there any particular shots/techniques it's associated with, and is there anything you'd recommend to get rid of the soreness/tightness? The only stretch that I've been recommended looks similar to the first picture on this page:http://www.yogajournal.com/for_teachers/2640
except it's done standing.

Thanks.
Yes, I believe I have a pretty complete offcourt training regimen. And it's not rehab I need, I'm not recovering from any injury, it's just a muscle that tends to get sore from playing. It's maybe a technique thing, I'm wondering if anyone else also has the same problem.

This same thing happens to me and I haven't figured out any way to treat it other than rest. It happens on the left side, all the way down the back, right about the bone above the glutes. Usually it is because of arching your back during kick serves and hitting too many kick serves. Backpain is very, very common to players who hit kick serves.

Mighty Matteo, thanks! I had a suspicion it was related to serves and more specifically kick serves. Other than rest, you should try stretching it before playing, it helped me anyway. But I guess the real solution is to stop arching the back so much on the serve... I wonder if other strokes are also involved.

Ramos77, I've seen physios, osteos, chiros, ... everything. IMO they all have their merits, as each has a different approach. The problem is that it is very rare to find someone that's knowledgeable about tennis. So they'll help you fix the pain, but they won't help with the underlying problem that's causing it (tennis).

stretch at least 5 times a day for 1 min. squat all the way down. heels right near the sit bones and feet pointing outward about 80 degree between. try to go as low as possible and balance for a min. one of the best lower back stretch. and reach out your arms in front for balance and more back stretch. lean the arms left and right for the opposite side lower back stretch.